High purity nitrogen gas is finding increasing use as a blanketing or inerting gas in the manufacturing of high value components, such as semiconductors, where freedom from contamination by oxygen is critical to the manufacturing process. Typically the high purity nitrogen is produced by the cryogenic rectification of air and piped directly to the semiconductor manufacturing plant. While such cryogenic air separation plants are highly reliable, these plants, like all production facilities, are subject to disruptions which could cause a reduction or stoppage of the high purity nitrogen flow from the cryogenic air separation plant to the semiconductor manufacturing plant. To avoid the catastrophic consequences of such a flow reduction or stoppage, high purity nitrogen plants have a liquid storage tank filled with liquid high purity nitrogen which can be quickly vaporized and passed on to the semiconductor manufacturing plant if the need arises.
While the high purity nitrogen plant may be able to produce some high purity nitrogen as liquid, at best it can produce only small quantities of such liquid. Accordingly, it is conventional practice to bring liquid high purity nitrogen to the storage tank by tanker truck or other transport means from a distant high purity liquid nitrogen production plant. While this conventional practice serves the intended purpose of maintaining the storage tank filled with liquid high purity nitrogen in case the need for its use arises, it is costly and cumbersome. It is desirable to have a facility which can produce high purity nitrogen gas and can also produce relatively large quantities of high purity nitrogen liquid so that transport of such liquid to the facility may be eliminated.
Accordingly, it is an object of this invention to provide a cryogenic rectification system which can produce relatively large quantities of both high purity nitrogen gas and high purity nitrogen liquid.